Such a device is known from DE-OS 35 34 768. The exposure of the photoconductor in this device occurs during the recording through a slot diaphragm the direction of the slot being parallel to the axis of rotation and which limits the X-ray beam to a narrow fan-shaped X-ray beam which passes through the examination area and exposes a narrow strip on the surface of the photoconductor. During the recording the carrier rotates about the axis of rotation and is moved synchronously therewith at right angles to the axis of rotation so that the examination area is projected sequentially on the surface of the photoconductor.
The reading of the charge pattern produced in this manner occurs immediately after the X-ray picture. The carrier rotates at a substantially higher speed than during the X-ray recording, and the reading device reads with one or more probes the charge on a substantially circular track on the surface of the photoconductor. In order to be able to read the whole surface, the reading unit is moved parallel to the axis of rotation at a comparatively lower average speed.
In such a device the reading can be done substantially more quickly, more precisely and more accurately than is possible with a flat photoconductor plate as it is known from the American patent U.S. Pat. No. 4,134,137. However, the fast reading is absolutely required, because the photoconductor discharges not only by the X-ray exposure but also by dark currents. On the other hand there is the disadvantage that the overall exposure time is comparatively long and that the power of the X-ray tube is used inefficiently, because only a thin radiation fan is always used for the exposure of the photoconductor.
It is to be noted that a device for producing X-ray pictures is already known from European patent application EP 94 843, in particular FIG. 8, in which a storage phosphor is provided on a cylindrical carrier which during taking the X-ray picture is stationary. Such storage phosphors lose their picture information considerably more slowly than photoconductors, so that a fast reading is not necessary. After each X-ray exposure, the carrier is rotated once about the axis of rotation in three steps, in which in the first step the X-ray picture is read with a two-dimensionally guided laser beam and in the subsequent step the storage phosphor is erased. In each step a further picture may be taken. So here the carrier stands still both during taking the X-ray picture and also during the reading process; reading cannot be done faster than in a flat record carrier.